A typical circuit board includes vias (or plated through-holes) and pads which solder to pins to provide electrical access to particular conductors of the circuit board (e.g., signal conductors, power planes, ground planes, etc. of the circuit board). The pins can belong to an external circuit board component such as an integrated circuit (IC), or can be standalone to enable external access for testing purposes. A conventional standalone pin is described in U.S. Pat. No. 6,179,631, entitled xe2x80x9cELECTRICAL CONTACT FOR A PRINTED CIRCUIT BOARDxe2x80x9d by Downes et al., the teachings of which are hereby incorporated by reference in their entirety.
Some circuit boards further include non-conductive holes (i.e., non-plated holes) through which large screws attach in order to support relatively large circuit board components. A conventional screw has a relatively uniform cylindrical shape with a larger-sized head. For example, to secure a row of connectors along an edge of a circuit board, some circuit board manufacturers drill holes along the edge, and insert such screws through the connectors and then through the drilled holes. The manufacturers then fasten nuts to the ends of the screws to firmly attach the connectors to the edge of the circuit board. As a result, stresses placed on the connectors are largely distributed through the screws to the circuit board rather than through more-fragile electrical connections between the circuit board and the connectors (e.g., rather than between circuit board vias and press-fit connector pins). Accordingly, the electrical connections between the circuit board and the connectors are unlikely to sustain damage during moments of high stress such as when the connectors of the circuit board mate with corresponding connectors of another circuit board (e.g., when the circuit board plugs into a backplane or motherboard).
Another common location for non-conductive holes on a circuit board is around interior component mounting locations. For example, a manufacturer can place screws through such non-conductive holes in order to attach a heat sink over one or more circuit board components. As another example, the manufacturer can place screws through non-conductive holes of a main circuit board to mount a relatively smaller secondary circuit board, e.g., a miniature circuit board with surface mount components called a multi-chip module (MCM), as is commonly done when attaching power converter circuitry to a main circuit board. As yet another example, when a circuit board component is soldered to an array of vias, the manufacturer can temporarily fasten alignment posts through non-conductive holes around the array of vias so that the alignment posts extend from the side of the circuit board opposite the component, and then lower a test fixture (e.g., a bed of nails) over the alignment posts to sample input and output signals of the component through the array of vias.
It should be understood that industry standards exist which specify particular mounts of conductor clearances that circuit board manufacturers must provide around vias and non-conductive holes. For example, the Institute for Interconnecting and Packaging Electronic Circuits (IPC) of Northbrook, Ill. defines Class 1 for home products, Class 2 for commercial grade products and Class 3 for military and high-reliability products. As another example, Underwriters Laboratories Inc. (UL) of Northbrook, Ill. sets related standards for such clearance areas. These clearance areas (i.e., non-conductor zones) are commonly referred to as xe2x80x9canti-padsxe2x80x9d. A manufacturer is not permitted to place electrical conductors (e.g., signal conductors, power planes, ground planes, etc.) within the anti-pad of a non-conductive hole unless that manufacturer is willing to avoid complying with the standard. Similarly, a manufacturer is only permitted to place the electrical conductor connecting to the via within the anti-pad of that via unless that manufacturer is willing to avoid complying with the standard.
Unfortunately, there are deficiencies associated with the above-described approaches to placing circuit board components on circuit boards using screws through drilled non-conductive holes. In particular, the anti-pads for such holes are quite large. For example, for a typical #8-32 (UNC) screw in certain applications, the anti-pad can be roughly a quarter of an inch or more. These relatively large anti-pads makes placement of conductors (e.g., signal etch) within the circuit board difficult especially in high density areas of etch such as around Ball Grid Array (BGA) component mounting locations, along a connector edge of the circuit board, etc. Circuit board manufacturers often have to re-route etches, and occasionally need to add wires or additional layers to the circuit boards in order to manufacture circuit boards in compliance with industry anti-pad standards.
The reason for the large anti-pads is that the diameters of the screws themselves are rather thick. Unfortunately, if the manufacturer used thinner screws, the thinner screws would not provide adequate stiffness and strength required for many applications. For example, the manufacturer would no longer be able to properly position and maintain many types of circuit board components such as connectors, mounting multi-chip modules (MCMs) or heat sinks, test fixtures, etc. when using thinner screws.
In contrast to the above-described conventional approaches to positioning circuit board components on circuit boards using screws which require relatively large anti-pads, the invention is directed to techniques for disposing circuit board components on circuit boards using pins which are configured to solder to the circuit boards. Soldering portions of the pins have relatively narrow diameters thus reducing the required anti-pad diameters. As a result, the circuit board manufacturer can maintain compliance with anti-pad industry standards, as well as adequately fasten the pins to the circuit boards with significant stiffness and strength. Engagement portions of the pins which extend from the circuit boards can have wider diameters in order to provide suitable rigidity for disposing a variety of circuit board components on the circuit boards.
One embodiment of the invention is directed to a pin for soldering to a circuit board. The pin includes a soldering portion which is configured to solder to a via of the circuit board and an engagement portion which is configured to engage with a circuit board component. The soldering portion has a circular cross-section and a soldering portion diameter. Similarly, the engagement portion has a circular cross-section and an engagement portion diameter. The soldering portion diameter is substantially narrower than the engagement portion diameter. Accordingly, the soldering portion can solder to relatively narrow circuit board via having a small anti-pad, and the thicker engagement portion can provide suitable strength for positioning the circuit board component in a reliable manner.
It should be understood that, since the circuit board can have smaller anti-pads around the mounting locations of the such pins, it is less difficult for the circuit board manufacturer to place etches around these mounting locations. Accordingly, it is less likely that the manufacturer will need to move etches or add wires or circuit board layers to comply with anti-pad industry standards. Moreover, the etches can be more openly and evenly distributed to promote better signal integrity due to the larger distances between signal etches and to provide fewer etch positioning constraints.
In one arrangement, the soldering portion of the pin is tapered so that becomes narrower toward the engagement portion. That is, the soldering portion has a first end which is nearer the engagement portion of the pin, and a second end which is further from the engagement portion. The first end has a narrower diameter than that of the second end. Accordingly, during the pin soldering process, there is more space around the via openings for gas to percolate and escape thus (i) minimizing the likelihood of trapping gas in the via, and (ii) enabling formation of a robust solder joint.
In one arrangement, the engagement portion of the pin is fashioned into a standardized end similar to a conventional screw and/or alignment post. Accordingly, circuit boards including the pin (or multiple pins) can accommodate conventional circuit board components such as test fixtures, heat sinks, circuit board modules (e.g., MCMs), connectors, frames, and supports.